NEREIS 57 



The appendages in annelids are called parapodia. Carefully 

 examine the parapodia at different parts of the body and see if 

 they are all alike. 



Remove a parapodium from the middle of the body ; mount 

 it on a slide in glycerine or water and study it with the aid of a 

 hand lens or a microscope. Compare it with the parapodia still 

 on the animal and determine which is its dorsal and which its 

 ventral side. It can be divided into two distinct portions, the 

 dorsal and the ventral portions, called the notopodium and the 

 neuropodium, respectively, each of which is stiffened by an inter- 

 nal chitinous supporting rod, called the aciculum. Find the two 

 acicula. The large dorsal lobe of the notopodium is a respira- 

 tory organ, a gill. It contains branching blood vessels which 

 can be easily seen. Attached to its dorsal edge is a slender, 

 vibratile sense-organ, the dorsal cirrus. Beneath the gill are two 

 lobes, one bearing bristles or setae. The neuropodium is made 

 up of two lobes, one of them setse-bearing, beneath which is a 

 ventral cirrus. 



Exercise 5. Draw a parapodium on a scale of 6 and label the 

 parts. 



Remove a parapodium from the hinder end of the animal, 

 mount it, and study it. Has it the same parts, and if not, 

 which are missing? 



Exercise 6. Draw it on a scale of 6. 



Internal anatomy. Make an incision with fine, sharp scissors 

 in the mid-dorsal line of the integument of the anterior third of 

 the animal, taking great care not to injure the viscera which lie 

 beneath. The body will be seen to be divided into compart- 

 ments corresponding to the somites, by transverse partitions 

 which are called septa. Holding the cut edge of the integument 

 with forceps, cut the septa where they join it, and then spread 

 out and pin down the body-wall, using many pins on each side. 



